HD 93129A has a close neighbour within the same young cluster, an O3 supergiant (HD 93129B). In addition, HD93129A itself has recently been found to be a close binary, with the fainter companion being yet another very hot O3 star. The exact nature of the two components is not known accurately but they have been calculated to be 0.9 magnitudes apart in brightness and of similar (high) masses.[3] Luminosity data is still quoted here for the two stars combined but the actual luminosity of the primary will be only a little over half that value.